Solid polymer type fuel cells are fuel cells in which a solid polymer solid electrolyte is interposed between an anode and a cathode and from which electricity is taken out by the mechanism that a fuel is supplied to the anode, oxygen or air is supplied to the cathode, and oxygen is reduced in the cathode. As the fuel, hydrogen, methanol or the like is mainly used.
In order to increase a reaction rate of a fuel cell and enhance energy conversion efficiency of a fuel cell, a layer containing a catalyst (also referred to as a “catalyst layer for fuel cell” hereinafter) has been provided on a cathode (air electrode) surface or an anode (fuel electrode) surface of the fuel cell in the past.
As the catalyst, a precious metal is generally used, and of such precious metals, precious metals that are stable at high potentials and have high activity, such as platinum and palladium, have been mainly used. However, prices of these precious metals are high and their resource quantity has a limit, and therefore, development of substitutable catalysts has been desired.
Moreover, there are problems that the precious metals used for the cathode surface sometimes dissolve in an acidic atmosphere and they are unsuitable for uses that need durability over a long period of time. On this account, development of catalysts that are not corroded in an acidic atmosphere, have excellent durability and have a high oxygen reduction ability has been eagerly desired.
Under such circumstances as above, studies of transition metal compounds, particularly transition metal carbonitrooxides, as the substitute catalysts for precious metals, have been promoted. These transition metal materials are inexpensive and their resources are abundant as compared with the precious metal materials such as platinum.
The conventional production process for transition metal carbonitrooxides is generally a process in which a transition metal compound and compounds capable of becoming a carbon source, a nitrogen source and an oxygen source are calcined. By mixing a transition metal carbonitrooxide produced by such a production process with carbon black or the like, a catalyst for a fuel cell is obtained.
In the case of using a transition metal carbonitrooxide produced by the above production process, an electrode catalyst for a fuel cell exhibiting performance of a certain level has been obtained, but an electrode catalyst for a fuel cell exhibiting practically satisfactory performance has not been necessarily obtained.
In a patent literature 1, a method to support a metal oxide on carbon has been reported. This method, however, is a method for producing carbon having excellent durability, not a method for producing an electrode catalyst for a fuel cell using a substitute for a precious metal.
In a non patent literature 1, a production process for a catalyst supported on carbon particles using a polymer complex method has been reported.
In the production process described in the non patent literature 1, however, a nitrogen-containing organic compound is not used as the organic compound contained, and an electrode catalyst for a fuel cell exhibiting satisfactory performance has not been obtained.